1. Field of the Invention
The present invention relates to a resonant cavity electron accelerator.
It has uses in the irradiation of various substances such as agro-alimentary products, either directly by electrons, or by X-rays obtained by conversion on a heavy metal target.
2. Description of the Background
A resonant cavity electron accelerator is already known from documents (1) to (3) which, like the other documents cited hereinafter, are listed at the end of the present description.
A specific embodiment of such a known accelerator called the "Rhodotron" (registered trade mark) is diagrammatically shown in longitudinal sectional form in FIG. 1 and in cross-section in FIG. 2. It comprises a high frequency source SHF, an electron source K, a coaxial cavity CC and two electron deflectors D1 and D2. The coaxial cavity CC is formed by an external cylindrical conductor 10 and an internal cylindrical Conductor 20, as well as two flanges 31 and 32. Said cavity has an axis A and a median plane Pm perpendicular to the axis A.
Among all the possible resonance modes of such a cavity, there is one, the so-called fundamental mode of the transverse electric type, for which the electrical field E is purely radial in the median plane and decreases on either side of the median plane and is then eliminated on the flanges 31 and 32. Conversely, the magnetic field H is at a maximum along the flanges and is eliminated in the median plane on changing direction.
The cavity CC is supplied by the high frequency source SHF using a loop 34. The electron source K emits an electron beam Fe, which is contained in a plane perpendicular to the axis of the coaxial cavity CC, the plane Pm in the example shown in FIG. 2. This plane meets the axis of the coaxial cavity at a point 0. The electron beam Fe penetrates the cavity CC through an opening 11 and traverses the cavity CC in accordance with a first diameter d1 of the external conductor 10. The internal conductor 20 has two openings 21, 22, which are diametrically opposite and which are successively traversed by the beam.
The electron beam is accelerated by the electrical field if the phase and frequency conditions are satisfied (said electrical field must remain in a direction opposite to the speed of the electrons). The accelerated beam then passes out of the coaxial cavity CC through an opening 12, which is diametrically opposite to the opening 11 and is then deflected by the deflector D1. The beam is reintroduced into the cavity CC by an opening 13 and then follows a second diameter D2 and undergoes a second acceleration in the coaxial cavity CC. It passes out through an opening 14, which is diametrically opposite to the opening 13.
On passing out, the beam is again deflected by the deflector d2 and reintroduced into the coaxial cavity CC by an opening 15. It then follows a third diameter d3 and undergoes a third acceleration and then passes out of the coaxial cavity CC via an opening 16 diametrically opposite to the opening 15.
Thus, the Rhodotron (registered trade mark) can be designed in such a way that the electron beam which it accelerates reenters and exits the coaxial cavity CC a larger number of times.
FIG. 3 diagrammatically shows a constructional embodiment of the high frequency source SHF. which makes it possible to supply the cavity CC with high frequency electromagnetic energy.
The source SHF of FIG. 3 comprises a power oscillator tube 36, a pilot oscillator 38, which emits a high frequency signal for controlling the grid of the tube 36 after having been amplified by an amplifier 40, a resonant cavity 42 to which is coupled the plate of the tube 36 and another resonant cavity 44 which adapts the impedance of the source SHF to a transmission line 46, which makes it possible to couple the source SHF to the coaxial cavity CC by means of the coupling loop 34. Such a source SHF is relatively complex and costly and gives rise to reliability problems.